Diaspirin crosslinked hemoglobin improves systemic oxygen uptake in oxygen supply-dependent septic rats

Caffeic acid: an antioxidant with novel antisickling properties

It is well documented that caffeic acid (3,4‐dihydroxycinnamic acid) (CA) interacts with and inhibits the oxidative reactions of myoglobin (Mb) and hemoglobin (Hb), and this interaction underlies its antioxidative action in meat. Sickle cell hemoglobin (HbS) is known for its tendency to oxidize more readily than normal HbA in the presence of hydrogen peroxide (H₂O₂), which leads to a more persistent and highly oxidizing ferryl Hb (HbFe⁴⁺). We have investigated the effects of CA on HbS oxidation intermediates, specifically on the ferric/ferryl forms. At a low concentration of H₂O₂ (0.5‐fold over heme), we observed a fivefold reduction in the amount of HbFe⁴⁺ accumulated in a mixture of ferric and H₂O₂ solution. Higher levels of H₂O₂ (onefold and twofold over heme) led to a lesser threefold and twofold reduction in the content of HbFe⁴⁺, respectively, possibly due to the saturation of the binding sites on the Hb molecule. The most intriguing finding was that when 5‐molar excess CA over heme was used, and a considerable increase in the delay time of HbS polymerization to approximately 200 s was observed. This delay in polymerization of HbS is theoretically sufficient to avoid microcapillary blockage and prevent vasoconstrictions in vivo. Mass spectrometry analysis indicated that CA was more extensively covalently bonded to βCys⁹³ than to βCys¹¹² and αCys¹⁰⁴. The dual antioxidant and antisickling properties of CA may be explored further to maximize its therapeutic potential in SCD.

Red blood cell storage duration and mortality in patients undergoing percutaneous coronary intervention

BACKGROUND

Blood transfusion has been associated with an increased mortality in patients undergoing percutaneous coronary intervention (PCI). Although the reasons for this remain unclear, it may be related to the structural and functional changes occurring within red blood cells (RBCs) during storage. We investigated whether RBC storage duration was associated with mortality in patients requiring transfusion after PCI.

METHODS

We collected data on all RBC transfusions occurring within 10 days of PCI (excluding those related to cardiac surgery) using the British Columbia Cardiac Registry and Central Transfusion Registry. Transfusion details were analyzed according to 30-day survival.

RESULTS

From a total of 32,580 patients undergoing PCI, 909 (2.8%) patients received RBCs with a mean storage duration of 25 +/- 10 days. In these 909 patients, mean transfusion volumes were lower in survivors (2.8 +/- 2.1 vs 3.8 +/- 2.9 U, P = .002) than those who died within 30 days. In a multivariate analysis to adjust for baseline risk, mean RBC storage age (HR 1.02 [95% CI 1.01-1.04], P = .002) and transfusion volume (HR 1.26 [95% CI 1.18-1.34], P < .001) both predicted 30-day mortality. Transfused patients who received only older blood (RBC min age >28 days) appeared to be at greater risk of death (HR 2.49 [95% CI 1.45-4.25], P = .001).

CONCLUSION

Red blood cell transfusion is associated with increased 30-day mortality in patients undergoing PCI. Although current transfusion practice permits RBC storage for up to 42 days, the use of older red cells may pose an additional hazard to this patient group.

Effects of levosimendan and dobutamine on experimental acute lung injury in rats

The effects of levosimendan on acute lung injury induced by peritonitis and abdominal hypertension in the early stages of sepsis in rats were investigated. Twenty-four adult male Wistar rats were randomized into: (1) sham, (2) subjected to abdominal hypertension and peritonitis induced lung injury using cecal ligation and puncture, then treated by dobutamine, (3) subjected to abdominal hypertension and peritonitis induced lung injury using cecal ligation and puncture, then treated by levosimendan, and (4) controls subjected to abdominal hypertension and peritonitis induced lung injury using cecal ligation and puncture with no treatment. In the control and levosimendan groups, cecal ligation and puncture resulted in moderate IL-1beta immunolabelling in lung tissue; marked IL-1beta immunolabelling was demonstrated in the dobutamine group. TNF-alpha immunolabelling was negative in both the sham and levosimendan groups, but moderate and weak immunoreactivities were observed in the dobutamine and control groups, respectively. There were almost no TUNEL positive cells in the sham, but they were prominent in the control. TUNEL positive cells were significantly less in the levosimendan treated lungs when compared to control and dobutamine groups. Immunoreactivity of eNOS was stronger in the dobutamine group when compared with the levosimendan group. In addition, iNOS immunoreactivity was strongly detected in the control group; this immunoreactivity was less in the levosimendan group than the dobutamine group. In this experimental sepsis model, treatment with levosimendan had a marked effect on attenuating or decreasing apoptosis and inflammation in the lung.

Potential uses of hemoglobin-based oxygen carriers in critical care medicine

Hemoglobin-based oxygen carriers (HBOCs) were initially developed to provide an alternative to blood transfusion. With the realization that hemoglobin solutions not only are red blood cell substitutes but also have a number of additional properties, including hemodynamic effects related to their oncotic and nitric oxide-scavenging effects, the broader concept of "hemoglobin therapeutics" was born. Promising effects on oxygen transport and the microcirculation need to be confirmed, and the results of studies with newer, second-generation HBOCs are eagerly awaited. In the meantime, possible adverse effects need to be carefully evaluated before HBOCs can be widely used in the ICU, emergency room, or prehospital setting.

Blood substitutes: hemoglobin-based oxygen carriers

Blood product substitutes, particularly the hemoglobin-based oxygen carriers, represent one of the most exciting fields of research and development in modern medicine. The concept has been several decades in the making, and with products in phase III clinical trials, the use of hemoglobin-based oxygen carriers may be close to reality. The potential applications are limitless with interest from the military and civilian sectors.

Modified haemoglobins and perfluorocarbons

After decades of research activities and product improvements in the field of artificial oxygen carriers based on either haemoglobin modifications or perfluorocarbon emulsions, these products have reached a critical stage of their development. Varieties of haemoglobin-based oxygen carriers and perfluorocarbon emulsions are under current clinical investigation. Although the clinical availability of artificial oxygen carriers may result in profound changes of fluid resuscitation from haemorrhage, the transfusion of human blood components as an integral part of medical trauma management will not be replaced. However, a rapid and effective restoration of tissue oxygenation by the use of artificial oxygen carriers in the treatment of severe haemorrhage may bridge time delays until stored and cross-matched human packed red cells are available. Whether artificial oxygen carriers could provide additional clinical benefits by sustaining tissue oxygenation even under conditions of a disturbed macro- or microcirculation is the subject of current investigations. Therefore, the application of safe and effective artificial oxygen carriers would not only be restricted to the treatment of severe haemorrhage, but additional therapeutic indications of artificial oxygen carriers in emergency medicine, trauma anaesthesia and other medical specialities would emerge.

Clinical consequences of red cell storage in the critically ill

Red cell (RBC) transfusions are a potentially life-saving therapy employed during the care of many critically ill patients to replace losses in hemoglobin to maintain oxygen delivery to vital organs. During storage, RBCs undergo a series of biochemical and biomechanical changes that reduce their survival and function. Additionally, accumulation of other biologic by-products of RBC preservation may be detrimental to recipients of blood transfusions. Laboratory studies and an increasing number of observational studies have raised the possibility that prolonged RBC storage adversely affects clinical outcomes. In this article, the laboratory and animal experiments evaluating changes to RBCs during prolonged storage are reviewed. Subsequently, the clinical studies that have evaluated the clinical consequences of prolonged RBC storage are reviewed. These data suggest a possible detrimental clinical effect associated with the transfusion of stored RBCs; randomized clinical trials further evaluating the clinical consequences of transfusing older stored RBCs are required.

MICROVASCULAR PERSPECTIVE OF OXYGEN-CARRYING AND -NONCARRYING BLOOD SUBSTITUTES

The development of an alternative to natural blood has evolved from the initial goal of replicating blood properties to the current objective of formulating a fluid that can be used to replace blood while preserving microvascular function and delivering oxygen. The properties of this fluid are counterintuitive and different from blood because it has high viscosity, oxygen affinity, and a low oxygen carrier concentration when compared with blood. The optimal oxygen carrier devised presently is poly-ethylene-conjugated human hemoglobin, a material demonstrated to be vasoinactive and void of the toxicities present in previous hemoglobin formulations. A feature of this material is that it is effective in small quantities, and therefore amplifies the equivalent supply of blood derived from blood donations.

[Artificial oxygen carriers as an alternative to red blood cell transfusion]

The expected cost-explosion in transfusion medicine (increasing imbalance between donors and recipients, treatment of transfusion-associated complications) increases the socio-economic significance of the development of safe and effective synthetic oxygen carriers as an alternative to the transfusion of allogeneic red blood cells. Currently two types of artificial oxygen carriers have been tested for safety and efficacy in cases of severe anemia otherwise requiring transfusion. Solutions based on human or bovine hemoglobin (HBOC) possess vasoconstrictor properties in addition to their oxygen transport capacity. The impact of vasoconstriction on tissue perfusion and organ function is however not yet fully understood. Nevertheless, in 2001 the bovine HBOC Hemopure was approved in South Africa for treatment of acutely anemic surgical patients. The purely synthetic perfluorocarbon (PFC) emulsions increase the physically dissolved portion of arterial oxygen content. Due to their particulate nature (emulsion droplets) PFCs may only be infused in low doses to avoid overload and malfunction of phagocytic cells of the reticulo-endothelial system. As part of a multimodal blood conservation program (including normovolemic hemodilution and hyperoxia) the low-dose administration of Oxygent effectively increases intraoperative anemia tolerance. Although reduction of perioperative allogeneic blood transfusion has already been demonstrated for HBOC and PFC, the global clinical establishment of artificial oxygen carriers is not to be expected in the near future.

Current Status of Artificial o2 Carriers

This article describes currently evaluated artificial O2 carriers, summarizes their efficacy, and discusses their side effects, based on and restricted to published data. For compounds in phase III testing, approximately 500 to 1000 patients have been dosed, and similar numbers of control patients have been investigated. For compounds in phase I or II testing, the number of patients dosed is significantly less. Unfortunately, there is a significant amount of nonpublished data, which renders the overall assessment difficult, and the direct comparison among different types of artificial O2 carriers is significantly limited by the virtual nonexistence of studies that directly compare different products.

The effect of storage time of human red cells on intestinal microcirculatory oxygenation in a rat isovolemic exchange model*

OBJECTIVE

To determine whether the storage time of human leukodepleted red blood cell concentrates compromises intestinal microvascular oxygen concentration oxygen (muPo(2)) during isovolemic exchange transfusion at low hematocrit.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research institute laboratory.

SUBJECTS

Male Wistar rats.

INTERVENTIONS

Intestinal muPo(2) was determined by Pd-porphyrin phosphorescence life-time measurements.

MEASUREMENTS AND MAIN RESULTS

Rats were brought near to a state of oxygen supply dependency by hemodilution with a pasteurized plasma protein solution to a hematocrit of 14.3 +/- 1.1% (n = 24). Subsequently, an isovolemic exchange transfusion with human leukodepleted red blood cells, stored for 2-6 days (fresh, n = 8), 2-3 wks (intermediate, n = 8), or 5-6 wks (old, n = 8), was performed to determine whether intestinal muPo(2) would be preserved. Immunologic reactions were avoided by washing the red blood cell concentrates three times before use. Isovolemic exchange with fresh and intermediate red blood cells maintained muPo(2) whereas old cells decreased muPo(2) with 26%. Subsequent transfusion with red blood cells (hematocrit approximately 60%) until reaching a hematocrit of 32.4 +/- 2.1 % (n = 24) increased intestinal muPo(2) in all three groups to the same extent between 28% and 32%. No changes in red blood cell deformability, as determined by a Laser-assisted Optical Rotational Cell Analyzer, could be demonstrated during 5 wks of storage.

CONCLUSION

This study shows that at low hematocrit, the oxygen-delivering capacity of human red blood cells stored 5-6 wks is reduced compared with fresh cells and red blood cells stored for an intermediate period. Although red blood cells stored for 2-3 wks are completely devoid of 2,3-diphosphoglycerate, their oxygen-delivering capacity to the intestines was the same as fresh red blood cells. Our study showed that red blood cell deformability was preserved during storage, suggesting that other mechanisms may account for the observed decrease in oxygen delivery by red blood cells stored 2-3 wks.

Microvascular perfusion upon exchange transfusion with stored red blood cells in normovolemic anemic conditions

BACKGROUND

Transfusions are intended to augment oxygen-carrying capacity. The ability of fresh and stored red blood cells (RBCs) to maintain microvascular perfusion and oxygen delivery to the tissue has not been directly measured.

STUDY DESIGN AND METHODS

Microvascular responses to exchange transfusion with fresh and stored RBCs after acute isovolemic hemodilution with a plasma expander were investigated with the hamster window chamber model. In-vivo functional capillary density (FCD), blood flow, and high-resolution oxygen distribution in microvascular networks were measured by noninvasive methods.

RESULTS

Exchange transfusion with an RBC suspension after a 60 percent isovolemic hemodilution with dextran 70 (6% MW = 70 kDa) resulted in a hematocrit of 18 percent (5.6 +/- 0.2 g/dL hemoglobin [Hb]). All other systemic variables were unchanged. Stored RBCs (28 days in citrate-phosphate-dextrose-adenine-1) resuspended in fresh frozen plasma matched to the Hct and Hb concentration were exchange transfused until 25 percent of the circulating RBCs were stored RBCs. Stored RBCs reduced microvascular flow and FCD by 63 and 54 percent, respectively, of the level achieved when fresh RBCs were exchange transfused. Microvascular oxygen extraction by the stored RBC was 54 percent lower than that of the fresh RBCs. The tissue oxygen levels were 3.5 and 14.4 mmHg for the stored and fresh RBCs, respectively.

CONCLUSION

Circulation of stored RBCs in a hemodiluted animal resulted in significantly malperfused and underoxygenated microvasculature that was not detectable at the systemic level.

Bradykinin-Induced Pulmonary Vasoconstriction Is Time and Inducible Nitric Oxide Synthase Dependent in a Peritonitis Sepsis Model

In an isolated perfused lung model, bradykinin induced pulmonary vasoconstriction in rats made septic by the injection of lipopolysaccharide (LPS). To mimic the pathophysiology of sepsis in humans more closely, we investigated pulmonary endothelial injury in a peritonitis model (cecal ligation and perforation; CLP). Male Sprague-Dawley rats were randomly divided into nine groups (n = 6-8). LPS and CLP rats were compared after 6 h with and without treatment with a selective inhibitor of inducible nitric oxide synthase (iNOS), L-N(6)-(1-iminoethyl)-lysine. Time dependency was investigated in CLP-treated rats at 24 h. The pulmonary circulation was isolated and perfused with a constant flow after the rats' tracheas were intubated and ventilated. Bradykinin (1, 3, and 6 microg) was injected, and changes in perfusion pressure were measured. Lungs were harvested for Western blot analysis to determine the role of iNOS in pulmonary endothelial dysfunction. In contrast to CLP 24 h rats, dose-dependent bradykinin-induced pulmonary vasoconstriction was observed in LPS and CLP 6 h rats. Concomitant administration of L-N(6)-(1-iminoethyl)-lysine significantly attenuated this vasoconstriction in both groups. The iNOS protein was expressed in lung homogenates from LPS 6 h and CLP 6 h but not from CLP 24 h rats. Both sepsis models caused bradykinin-induced pulmonary vasoconstriction, with the CLP groups demonstrating a time dependency of this effect. In conjunction with the time-dependent decrease in iNOS protein, the attenuated bradykinin-induced vasoconstriction due to selective iNOS inhibition suggests an important role for iNOS in pulmonary endothelial injury for both sepsis models.

The Influence of Allogeneic Red Blood Cell Transfusion Compared with 100% Oxygen Ventilation on Systemic Oxygen Transport and Skeletal Muscle Oxygen Tension After Cardiac Surgery: Retracted

In this study we investigated the effects of allogeneic red blood cell (RBC) transfusion on tissue oxygenation compared with those of 100% oxygen ventilation by using systemic oxygen transport variables and skeletal muscle oxygen tension (PtiO2). Fifty-one volume-resuscitated, mechanically ventilated patients with a nadir hemoglobin concentration in the range from 7.5 to 8.5 g/dL after elective coronary artery bypass grafting were allocated randomly to receive 1 unit (transfusion 1; n = 17) or 2 units (transfusion 2; n = 17) of allogeneic RBCs and ventilation with 40% oxygen or pure oxygen ventilation (100% oxygen; n = 17) and no allogeneic blood for 3 hours. Invasive arterial and pulmonary artery pressures and calculations of oxygen delivery (oxygen delivery index) and consumption indices (oxygen consumption index) were documented at 30-min intervals. PtiO2 was measured continuously by using implantable polarographic microprobes. Systemic oxygen transport variables and PtiO2 were similar between groups at baseline. The oxygen delivery index increased significantly with transfusion of allogeneic RBCs and 100% oxygen ventilation, whereas the oxygen consumption index remained unchanged. Oxygen 100% ventilation increased PtiO2 significantly (from 24.0 +/- 5.1 mm Hg to 34.2 +/- 6.2 mm Hg), whereas no change was found after transfusion of allogeneic RBCs. Peak PtiO2 values were 25.2 +/- 5.2 mm Hg and 26.3 +/- 6.5 mm Hg in the transfusion 1 and 2 groups, respectively. Transfusion of stored allogeneic RBCs was effective only in improving systemic oxygen delivery index, whereas 100% oxygen ventilation improved systemic oxygen transport and PtiO2. This improved oxygenation status was most likely due to an increase in convective oxygen transport with a large driving gradient for diffusion of plasma-dissolved oxygen into the tissue.

Hemoglobin solutions

OBJECTIVE

To review current knowledge about cell-free hemoglobin solutions.

DATA SOURCE

A computerized MEDLINE search was used to retrieve all studies concerning cell-free hemoglobin solutions from 1990 to 2003. The reference lists of all available review articles and primary studies were also reviewed to identify references not identified in the computerized search.

STUDY SELECTION

All clinical and experimental studies involving cell-free hemoglobin solutions were included.

DATA EXTRACTION

From the selected studies, information was obtained regarding the experimental model or the study population in which cell-free hemoglobin solutions were investigated, the type of cell-free hemoglobin solution used, their deleterious or beneficial effects, and their possible indications.

DATA SYNTHESIS

In many studies, hemoglobin solutions were considered as efficient resuscitative agents and good alternatives to red blood cell transfusion, owing to their marked vasopressor effect, coupled with their capacity to improve the microcirculation and rapidly restore metabolic parameters. The main problems identified include excessive systemic vasoconstriction and oxidative damage. Initial enthusiasm in the development of hemoglobin solutions has been tempered recently by the negative results of a U.S. multicenter trial studying the early infusion of diaspirin cross-linked hemoglobin in trauma patients. Nevertheless, the properties of diaspirin cross-linked hemoglobin (and particularly the strong vasopressor effects) cannot be attributed to all hemoglobin solutions, and results of new clinical studies are eagerly awaited to evaluate the potential benefit of such solutions in the management of trauma patients.

CONCLUSIONS

Today, we are aware of the effects of the first generation of blood substitutes. Further research is ongoing into newer solutions. One area of interest is the development of new molecular structures to decrease nitric oxide binding, thus minimizing any adverse events and maximizing potential benefits. Nevertheless, possible adverse effects need to be carefully evaluated before these agents can be widely administered.

Effect of haemodilution with diaspirin cross-linked haemoglobin on the oxygen reserve in a rodent model of surgical blood loss

The efficacy of pre-operative haemodilution is limited by the reduction in haemoglobin concentration. Acellular haemoglobin-based oxygen carriers provide an alternative to colloid as a haemodiluent, potentially extending the safe limits of this procedure. The aim of this investigation was to determine whether haemodilution with a cross-linked haemoglobin solution, diaspirin cross-linked haemoglobin solution (DCLHb), would enhance the oxygen reserve compared to pentastarch. Sprague Dawley rats were placed in a metabolic box to directly measure systemic oxygen consumption (VO2). Rats were randomized to be haemodiluted to a cellular haemoglobin of 80 g L(-1) with either DCLHb or pentastarch. Oxygen reserve was assessed during isovolemic haemorrhage by determining the critical oxygen delivery (DO2crit) and haemoglobin concentration at the point of oxygen supply dependency (OSD). Following haemodilution and for the duration of the experiment, cardiac index (CI) was significantly lower and systemic vascular resistance was significantly higher in the DCLHb than the pentastarch group. The DO2crit (3.2 +/- 0.4 mL minAg(-1) and 3.4 +/- 0.5 mL minAg(-1), DCLHb versus pentastarch) and cellular haemoglobin concentration (51 +/- 9 g L(-1) and 48 +/- 9 g L(-1)), at which rats entered OSD were similar in both groups. Total haemoglobin concentration (cellular and plasma DCLHb) and arterial oxygen content were significantly higher in the DCLHb group (total haemoglobin, 66 +/- 8 g L(-1) and arterial content, 9.2 +/- 1.4 mL dL(-1)) compared to the pentastarch group (total haemoglobin, 48 +/- 9 g L(-1) and arterial content, 7.3 +/- 1.4 mL dL(-1)). Oxygen extraction ratios increased from baseline levels to 0.53 +/- 0.07 and 0.56 +/- 0.1, for the DCLHb and pentastarch groups, respectively, and were not significantly different. The increase in arterial oxygen content from DCLHb in plasma was offset by the decrease in CI observed in this group. Plasma DCLHb did not extend the limits of haemodilution beyond the capacity of the cellular haemoglobin concentration.

Small intestine intramucosal PCO(2) and microvascular blood flow during hypoxic and ischemic hypoxia

OBJECTIVE

To determine whether small intestine intramucosal PCO(2) and mucosal blood flow changes would be different between ischemic and hypoxic hypoxia.

DESIGN

Randomized animal experiment.

SETTING

Research laboratory.

SUBJECTS

Anesthetized, mechanically ventilated, and surgically instrumented pigs.

INTERVENTIONS

Systemic oxygen delivery was lowered in a stepwise manner to decrease it beyond critical oxygen delivery by lowering either FIO(2) or blood volume.

MEASUREMENTS AND MAIN RESULTS

In hypoxic hypoxia pigs (n = 6), arterial oxygen concentration and oxygen delivery decreases were achieved by progressively reducing arterial PO(2) while cardiac index remained unchanged. In ischemic hypoxia pigs (n = 5), oxygen delivery reduction was achieved by progressively reducing cardiac index while arterial PO(2) remained unchanged. In control pigs, oxygen delivery remained unchanged. The lowest oxygen delivery measured in both hypoxia and ischemia experiments was 3.60 +/- 0.26 vs. 2.93 +/- 0.77 mL x kg(-1) x min(-1), respectively (p =.23). At the lowest oxygen delivery level, differences between ischemic hypoxia and hypoxic hypoxia experiments were observed for arterial lactate concentration (468 +/- 308 vs. 1070 +/- 218 mmol/L, respectively; p =.03), mixed venous arterial PCO(2) difference (10 +/- 7 vs. 4 +/- 2 torr, respectively; p =.04), and small intestine mucosal blood flow (6.2 +/- 2.1 vs. 15.7 +/- 7.4 perfusion units, respectively; p =.02). Small intestine intramucosal-arterial difference was higher in ischemic hypoxia than in hypoxic hypoxia (52 +/- 15 vs. 31 +/- 12 torr, respectively; p =.03).

CONCLUSION

Small intestine intramucosal PCO(2) increases may indicate systemic oxygen uptake supply limitation in ischemic and hypoxic hypoxia related to conditions of mucosal flow stagnation and CO(2) generation.

The effect of the transfusion of stored RBCs on intestinal microvascular oxygenation in the rat

BACKGROUND

Although it is known that the transfusion of stored RBCs does not always improve tissue O(2) consumption under conditions of limited tissue oxygenation, the efficiency of O(2) delivery to the microcirculation by stored RBCs has never been determined.

STUDY DESIGN AND METHODS

In a rat hemorrhagic shock model, the effects of resuscitation with fresh or 28-day-old RBCs stored in CPD plasma, saline-adenine-glucose-mannitol, and CPDA-1 plasma were investigated. Systemic hemodynamic and intestinal oxygenation measures were monitored. Intestinal microvascular PO(2) was determined with the O(2)-dependent quenching of palladium-porphyrin phosphorescence, and the RBC deformability was measured with a Laser-assisted optic rotational cell analyzer.

RESULTS

Hemodynamic and oxygenation measures were significantly decreased during hemorrhagic shock. Intestinal oxygen consumption and mesenteric venous pO(2) were restored with the transfusion of both fresh and stored RBCs, except for CPD-stored RBCs. The intestinal microvascular pO(2) improved only with the transfusion of fresh RBCs. Deformability of the stored RBCs was significantly decreased.

CONCLUSION

In contrast to that of fresh RBCs, the transfusion of stored RBCs did not restore the microcirculatory oxygenation, possibly because of impaired O(2) unloading, but, except for CPD-stored RBCs, the storage-induced changes were not enough to impair intestinal VO(2) and mesenteric venous pO(2).

Influence of cell-free Hb on local tissue perfusion and oxygenation in acute anemia after isovolemic hemodilution

BACKGROUND

Oxygen-carrying solutions are intended to eliminate the blood transfusion trigger. Their ability to maintain microvascular perfusion and to deliver oxygen to tissue when they replace the RBCs as oxygen carriers has not been directly measured.

STUDY DESIGN AND METHODS

Microvascular response to exchange transfusion with a polymerized bovine cell-free Hb (PBH) solution after acute isovolemic hemodilution with a plasma expander was investigated by using the hamster window model. In vivo functional capillary density (FCD), blood flow, and high-resolution oxygen distribution in microvascular networks were measured by noninvasive methods.

RESULTS

Exchange transfusion of PBH solution after a 60-percent isovolemic hemodilution with dextran 70 (MW, 70 kDa) resulted in a Hct of 11 percent and a Hb content of 6.7 g per dL. FCD was 0.37 of baseline. Interstitial pO2 was reduced from 21.0 mm Hg to 0.3 mmHg. Arteriolar and venular blood flows were ratios of 0.75 and 0.76 relative to baseline. In a previous study, tissue pO2 after hemodilution to 5.6 g of Hb per dL with dextran 70 was 23.0 mmHg. Hypervolemic injection of PBH solution increased blood pressure and caused vasoconstriction.

CONCLUSION

Using PBH solution to replace RBC oxygen-carrying capacity during low Hb content conditions (<50%) causes abnormally low tissue oxygenation and FCD, while the same level of hemodilution with dextran maintains normal microvascular conditions.

Experimental and emerging therapies for sepsis and septic shock

The underlying principles of sepsis therapy have remained unchanged for decades. These include: prompt institution of antimicrobial agents aimed at the inciting pathogen, source control directed at removal of the infection nidus whenever possible, and support of organ dysfunction. Despite advances in antibiotics, surgical techniques and organ support technology, the morbidity and mortality from sepsis-related diseases have remained substantially unchanged (30 - 50%). Immunomodulation of the inflammatory cascade has been suggested as a crucial but inadequately addressed element in the treatment of sepsis. The list of potential therapeutic targets has been growing as more and more mediators are identified in the pathogenesis of sepsis. To date, numerous anti-inflammatory agents, found to have favourable effects in animal models of septic shock, have been tested in a number of clinical trials on thousands of patients. In this first of a three part series, we go through some of the background and current strategies in sepsis therapy. In this review, we include the two novel therapies that have shown clear survival benefit in large, randomised, placebo-controlled, multi-centre trials, low-dose steroids and recombinant activated protein C. Also included in this review are studies on antithrombin III, platelet-activating factor antagonists, complement modulators, nitric oxide synthase inhibitors and caspase inhibitors (apoptosis inhibitors).

Diaspirin crosslinked hemoglobin enables extreme hemodilution beyond the critical hematocrit

BACKGROUND

Normovolemic hemodilution is an effective strategy to limit perioperative homologous blood transfusions. The reduction of hematocrit related to hemodilution results in reduced arterial oxygen content, which initially is compensated for by an increase in cardiac output and oxygen extraction ratio. To increase the efficacy of hemodilution, a low hematocrit should be aimed for; however, this implies the risk of myocardial ischemia and tissue hypoxia.

OBJECTIVE

To assess whether hemodilution can be extended to lower hematocrit values by the use of a hemoglobin-based artificial oxygen carrier solution.

DESIGN

Prospective, randomized, controlled.

SETTING

Animal laboratory of a university hospital.

SUBJECTS

Twelve anesthetized, mechanically ventilated pigs.

INTERVENTIONS

Isovolemic hemodilution was performed with either 10% diaspirin crosslinked hemoglobin (DCLHb Baxter Healthcare, Boulder, CO; n = 6) or 8% human albumin solution (HSA, oncotically matched to DCLHb, Baxter Healthcare; n = 6) to a hematocrit of 15%, 8%, 4%, 2%, and 1%.

MEASUREMENTS AND MAIN RESULTS

In both groups, measurements were performed at baseline at the previously mentioned preset hematocrit values and at the onset of myocardial ischemia characterized by critical hematocrit (significant ST-segment depression >0.1 mV and/or arrhythmia). To determine peripheral tissue oxygenation and myocardial perfusion and function, the following variables were evaluated: total body oxygen transport variables, tissue oxygen partial pressure (tPo2, MDO-Electrode, Eschweiler Kiel, Germany) on the surface of the skeletal muscle, coronary perfusion pressure, left ventricular (LV) end-diastolic pressure, global and regional myocardial contractility (maximal change in pressure over time, LV segmental shortening, microsonometry method), LV myocardial blood flow (fluorescent microsphere technique), LV oxygen delivery, and the ratio between LV subendocardial and subepicardial myocardial perfusion. In the HSA group, critical hematocrit was found at 6.1 (1.8)% (hemoglobin, 2 g x dL(-1)), whereas all DCLHb-treated animals survived hemodilution until hematocrit 1.2 (0.2)% (hemoglobin, 4.7 g x dL(-1)) was achieved without signs of hemodynamic instability. Although arterial oxygen content was higher in the DCLHb group at 1.2% hematocrit than in the HSA group at critical hematocrit (i.e., hematocrit, 6.1%; hemoglobin, 2 g.dL-1) neither oxygen delivery and oxygen uptake nor median tPo2 and hypoxic tPo2 values on the skeletal muscle were different between groups. In contrast, subendocardial ischemia was absent in DCLHb-diluted animals until 1.2% hematocrit was achieved. This was attributable to a higher coronary perfusion pressure (65 (22) mm Hg vs. 19 (8) mm Hg; p <.05), higher subendocardial perfusion (4.1 (2.6) mL.min-1.g-1 vs. 1.2 (0.4) mL x min(-1) x g(-1)), and subendocardial oxygen delivery (5.7 (2) mL x min(-1) x g(-1), p <.05) in DCLHb-diluted animals, resulting in superior myocardial contractility reflected by maximal change in pressure over time (3829 (1914) vs. 1678 (730); p <.05) and higher regional myocardial contractility (11 (8)% vs. 6 (2)%; p <.05). An increased LV end-diastolic pressure reflected LV myocardial pump failure in HSA-diluted animals but was unchanged in DCLHb-diluted animals. In the DCLHb group, systemic vascular resistance index remained at baseline values throughout the protocol, whereas coronary vascular resistance decreased. In contrast, both variables decreased in HSA-diluted animals.

CONCLUSION

DCLHb as a diluent allowed for hemodilution beyond the hematocrit value, determined "critical" after hemodilution with HSA (6.1% (1.8)%). Even at 1.2% hematocrit (hemoglobin, 4.7 g x dL(-1)) myocardial perfusion and function were maintained, although at the expense of peripheral tissue oxygenation. This discrepancy in regional oxygenation might be caused by a redistribution of blood flow favoring the heart, which is related to a disproportionate decrease of coronary vascular resistance index during hemodilution with DCLHb.

Comparative effects of red blood cell transfusion and increasing blood flow on tissue oxygenation in oxygen supply-dependent conditions

Red blood cell (RBC) transfusion is usually administered to improve oxygen delivery (DO(2)) in order to sustain tissue oxygen demand. However, this practice is not supported by firm clinical or experimental data. Using a randomized two-period crossover design, this study compared the efficacy of "fresh" RBC transfusion and increased blood flow to restore tissue oxygenation in oxygen supply-dependent conditions. In 12 ketamine-anesthetized mongrel dogs submitted to nonpulsatile normothermic cardiopulmonary bypass, DO(2) was reduced by a progressive decrease in pump flow. DO(2) dependency was defined as an O(2) uptake (V O(2)) decrease by more than 15% from baseline value. Then, intervention consisted of a 40% increase in DO(2) obtained either by transfusion of "fresh" dog's RBC (stored < 3 d) or by increase in pump flow. Animals received both interventions sequentially in a random order, while O(2) saturation was maintained constant. In O(2) supply-dependent conditions, rising pump flow from 1.6 +/- 0.4 to 2.7 +/- 0.7 L/ min increased DO(2) from 5.4 +/- 1.1 to 9.0 +/- 1.3 ml/kg/min (p < 0.01) and V O(2) from 3.5 +/- 0.4 to 4.1 +/- 0.5 ml/kg/min (p = 0.02). "Fresh" RBC transfusion, which increased the hemoglobin concentration from 6.4 +/- 0.9 to 11.1 +/- 1.3 g/dl, increased DO(2) from 5.4 +/- 1.2 to 9.0 +/- 1.4 ml/kg/min (p < 0.01) and V O(2) from 3.6 +/- 0.4 to 4.1 +/- 0.5 ml/kg/min (p = 0.02). There was no difference in V O(2) resulting from both interventions. In oxygen supply-dependent conditions, "fresh" RBC transfusion and increased blood flow are equally effective in restoring tissue oxygenation.

Is a low transfusion threshold safe in critically ill patients with cardiovascular diseases?

OBJECTIVE

To compare a restrictive red blood cell transfusion strategy with a more liberal strategy in volume-resuscitated critically ill patients with cardiovascular disease.

SETTING

Twenty-two academic and three community critical care units across Canada.

STUDY DESIGN

Randomized controlled clinical trial.

STUDY POPULATION

Three hundred fifty-seven critically ill patients with cardiovascular diseases from the Transfusion Requirements in Critical Care trial who had a hemoglobin concentration of <90 g/L within 72 hrs of admission to the intensive care unit.

INTERVENTIONS

Patients were randomized to a restrictive strategy to receive allogeneic red blood cell transfusions at a hemoglobin concentration of 70 g/L (and maintained between 70 and 90 g/L) or a liberal strategy to receive red blood cells at 100 g/L (and maintained between 100 and 120 g/L).

RESULTS

Baseline characteristics in the restrictive (n = 160) and the liberal group (n = 197) were comparable, except for the use of cardiac and anesthetic drugs (p <.02). Average hemoglobin concentrations (85 +/- 6.2 vs. 103 +/- 6.7 g/L; p <.01) and red blood cell units transfused (2.4 +/- 4.1 vs. 5.2 +/- 5.0 red blood cell units; p <.01) were significantly lower in the restrictive compared with the liberal group. Overall, all mortality rates were similar in both study groups, including 30-day (23% vs. 23%; p = 1.00), 60-day, hospital, and intensive care unit rates. Changes in multiple organ dysfunction from baseline scores were significantly less in the restrictive transfusion group overall (0.2 +/- 4.2 vs. 1.3 +/- 4.4; p =.02). In the 257 patients with severe ischemic heart disease, there were no statistically significant differences in all survival measures, but this is the only subgroup where the restrictive group had lower but nonsignificant absolute survival rates compared with the patients in the liberal group.

CONCLUSION

A restrictive red blood cell transfusion strategy generally appears to be safe in most critically ill patients with cardiovascular disease, with the possible exception of patients with acute myocardial infarcts and unstable angina.

Diaspirin cross-linked hemoglobin improves oxygen extraction capabilities in endotoxic shock

We studied the effects of diaspirin cross-linked hemoglobin (DCLHb), a cell-free hemoglobin derived from human erythrocytes, on blood flow distribution and tissue oxygen extraction capabilities in endotoxic shock. Eighteen pentobarbital sodium-anesthetized, mechanically ventilated dogs received 2 mg/kg of E. coli endotoxin, followed by saline resuscitation to restore cardiac filling pressures to baseline levels. The animals were randomly divided into three groups: six served as control, six received DCLHb at a dose of 500 mg/kg (group 1) and six DCLHb at a dose of 1,000 mg/kg (group 2). Cardiac tamponade was then induced by saline injection in the pericardial sac to progressively reduce cardiac index and thereby allow study of tissue oxygen extraction capabilities. DCLHb had a dose-dependent vasopressor effect but did not significantly alter cardiac index or regional blood flow. During cardiac tamponade, critical oxygen delivery was 12.8 +/- 0.7 ml. kg(-1). min(-1) in the control group, but 8.6 +/- 0.9 and 8.2 +/- 0.7 ml. kg(-1). min(-1) in groups 1 and 2, respectively (both P < 0.05 vs. control group). The critical oxygen extraction ratio was 39.1 +/- 3.1% in the control group but 58.7 +/- 12.8% and 60.2 +/- 9.0% in groups 1 and 2, respectively. We conclude that DCLHb can improve whole body oxygen extraction capabilities during endotoxic shock in dogs.

Diaspirin cross-linked Hb and norepinephrine prevent the sepsis-induced increase in critical O(2) delivery

We hypothesized that support of arterial perfusion pressure with diaspirin cross-linked Hb (DCLHb) would prevent the sepsis-induced attenuation in the systemic O(2) delivery-O(2) uptake relationship. Awake septic rats were treated with a chronic infusion of DCLHb or a reference treatment [norepinephrine (NE)] to increase mean arterial pressure by 10-20% over 18 h. Septic and sham control groups received normal saline. Isovolemic hemodilution to create anemic hypoxia was then performed in a metabolic box during continuous measurement of systemic O(2) uptake. O(2) delivery was calculated from hemodynamic variables, and the critical point of O(2) delivery (DO(2 crit)) was determined using piecewise regression analysis of the O(2) delivery-O(2) uptake relationship. Sepsis increased DO(2 crit) from 4.99 +/- 0.17 to 6.69 +/- 0.42 ml x min(-1) x 100 g(-1) (P < 0.01), while O(2) extraction capacity was decreased (P < 0.05). DCLHb and NE infusion prevented the sepsis-induced increase in DO(2 crit) [4.56 +/- 0.42 ml x min(-1) x 100 g(-1) (P < 0.01) and 5.04 +/- 0.56 ml x min(-1) x 100 g(-1) (P < 0.05), respectively]. This was explained by a 59% increase in O(2) extraction capacity in the DCLHb group compared with septic controls (P < 0.05), whereas NE treatment decreased systemic O(2) uptake in anemic hypoxia (1.51 +/- 0.08 vs. 1.87 +/- 0.1 ml x min(-1) x 100 g(-1) in septic controls, P < 0.05). We conclude that DCLHb ameliorated O(2) extraction capacity in the septic microcirculation, whereas NE decreased the metabolic demands of the tissues.

Hemoglobin solutions--not just red blood cell substitutes

OBJECTIVE

To review current knowledge about cell-free hemoglobin solutions.

DATA SOURCES

All studies involving cell-free hemoglobin were retrieved from a computerized MEDLINE search from 1980 to 1998. We also reviewed the reference lists of all available review articles and primary studies to identify references not found in the computerized search.

STUDY SELECTION

Clinical and experimental studies in which cell-free hemoglobin solutions were studied.

DATA EXTRACTION

From the selected studies, information was obtained regarding the experimental model or the study population in which cell-free hemoglobin solutions were investigated, the type of cell-free hemoglobin solution, their deleterious or beneficial effects, and their possible indications.

DATA SYNTHESIS

In many studies, hemoglobin solutions were considered as efficient resuscitative agents and good alternatives to red blood cell transfusion, because of their marked vasopressor effect coupled with their capacity to improve the microcirculation and quickly restore metabolic parameters. Nevertheless, potential problems include an increased susceptibility to infection, immunosuppression, oxidative damage, excessive pulmonary and systemic vasoconstriction, and platelet activation.

CONCLUSIONS

Hemoglobin solutions are more than mere blood substitutes. Promising effects on oxygen transport and the microcirculation need to be confirmed, and the results of continuing research are eagerly awaited.

Diaspirin cross-linked hemoglobin improves mucosal perfusion in the ileum of septic rats

OBJECTIVE

To determine the effect of a bolus infusion of diaspirin cross-linked hemoglobin (DCLHb or hemoglobin crosfumaril) on the ileal mucosal microcirculation in septic rats.

DESIGN

Prospective, randomized, single-blinded study.

SETTING

University-affiliated animal research laboratory.

SUBJECTS

Twenty-four male Sprague-Dawley rats, weighing 320-380 g.

INTERVENTIONS

Under inhalational anesthesia, arterial and venous catheters were inserted and sepsis was created by cecal ligation and perforation (CLP). Twenty-four hours later, animals were reanesthetized and ventilated. Via midline abdominal incision, the ileum was mobilized and prepared for intravital microscopy. Post-CLP hemodynamic values were obtained, and videomicroscopy was performed on four to ten villi. Animals were then randomized to receive 2 mL of DCLHb solution (100 mg/mL; n = 12) or pentastarch (n = 12) intravenously, and measurements were repeated after 20 mins. Rats treated with DCLHb then received nitroprusside to restore mean arterial pressure to post-CLP levels, and final measurements were obtained 15 mins later.

MEASUREMENTS AND MAIN RESULTS

Cardiac index increased with both treatments (p < .001), whereas systemic vascular resistance index and mean arterial blood pressure were augmented only with DCLHb (p < .0001 compared with pentastarch). Intercapillary areas (ICA; inversely related to capillary density) were determined using computerized image analysis. ICA size decreased after treatment, from 974 +/- 79 to 791 +/- 106 microm2 with DCLHb and from 1044 +/- 90 to 840 +/- 82 microm2 with pentastarch (both p < .05). Red blood cell velocity in terminal arterioles, as assessed by velocimetry from the recorded images, increased by 15% with both treatments (p < .05). Restoration of mean arterial pressure to post-CLP levels in DCLHb animals by nitroprusside infusion abolished the effects of the hemoglobin solution on ICA size and red blood cell velocity.

CONCLUSION

Both DCLHb and pentastarch infusion improved microcirculatory perfusion in the ileum of septic rats. In addition, DCLHb also exhibited vasopressor properties, which in combination with improved perfusion may be particularly useful in the treatment of sepsis.

Tissue perfusion and oxygenation with blood substitutes

As an alternative to transfusion of red blood cells, intravenously (iv) administered artificial oxygen (O(2)) carriers are intended to increase the reduced O(2) carrying capacity of blood in the case of acute severe anemia, i.e. hemorrhagic shock or extreme normovolemic hemodilution (ANH). Actually, two groups of artificial O(2) carriers are investigated: ultrapurified, stroma-free hemoglobin solutions (SFH) of human or bovine origin and synthetically produced perfluorocarbons (PFC). SFH may be administered in large amounts and are suitable for 1:1 replacement of blood losses in case of hemorrhage as well as for isovolemic exchange of blood during ANH. In both situations SFH solutions effectively restore (hemorrhagic shock) and maintain (extreme ANH) tissue oxygenation despite extremely low hematocrit values. The vasopressor property of the isolated Hb molecule leads to a species-dependent (rodent>pig>human) increase in systemic and pulmonary vascular resistance, but leaves overall distribution of cardiac output uninfluenced. Due to the particulate nature of PFC emulsions, iv administration has to be restricted to small doses (3-4.5 ml/kg body weight for the actually investigated 60% w/v perflubron emulsion) in order to avoid overload of the reticuloendothelial system. Thus PFC emulsions are unsuitable for isovolemic blood replacement in hemorrhagic shock or ANH. Low-dose iv PFC administration in already hemodiluted subjects, however, creates an additional margin of safety to guarantee adequate tissue oxygenation which allows for further, extreme ANH, without risking tissue hypoxia.

Pre-separation storage of whole blood: the effect of temperature on red cell 2,3-diphosphoglycerate and myeloperoxidase in plasma

BACKGROUND

Although whole blood intended for component preparation is commonly left to cool at ambient temperature, knowledge is insufficient concerning what effects this may have on red blood cell (RBC) quality, in particular after a prolonged hold.

STUDY DESIGN AND METHODS

Whole blood collected in CPD was incubated at 20 degrees C and 28 degrees C for 6 h designed as a paired study. Blood components were prepared and the red blood cell concentrates (RBCs) were stored for 28 days at 4 degrees C +/- 2 degrees C. Blood gases, pH, glucose, lactate, adenosine triphosphate (ATP), 2,3-diphosphoglycerate (2,3-DPG) and plasma myeloperoxidase (MPO) were investigated.

RESULTS

After 6 h the 2,3-DPG concentrations had lowered to 88% (20 degrees C) and 54% (28 degrees C) of initial levels, respectively. The difference was significant and was maintained for 28 days, although, at low levels from day 7 (28 degrees C) and day 14 (20 degrees C) of storage. ATP was maintained at the initial level in both groups during the first 6 h of storage but after component separation the levels were significantly higher in the 28 degrees C group during the first 5 days. The release of myeloperoxidase (MPO) was significantly higher in the non-cooled group than in the cooled group.

CONCLUSIONS

Pre-separation holding for 6 h of whole blood at temperatures of 28 degrees C causes a great and rapid loss of 2,3-DPG and considerable formation of acid metabolites resulting in clearly subnormal 2,3-DPG levels even on day 1. Active pre-separation cooling to 20 degrees C is to be recommended.

Factors influencing the individual effects of blood transfusions on oxygen delivery and oxygen consumption

OBJECTIVE

To determine factors influencing the individual effects of blood transfusions regarding oxygen delivery and consumption.

DESIGN

Chart review.

SETTING

A university hospital cardiosurgical intensive care unit.

PATIENTS

Sixty-seven patients with 170 transfusion events evaluated.

INTERVENTIONS

Blood transfusion.

MEASUREMENTS AND MAIN RESULTS

Measurements were performed before and after a blood transfusion, separated by 302 +/- 13 mins (mean +/- SEM). The individual increase in cardiac index resulting from a blood transfusion was inversely related to cardiac index before transfusion (p < .001), oxygen delivery index before transfusion (p < .001), and oxygen consumption index before transfusion (p < .001). The individual increase in oxygen delivery index was inversely related to oxygen consumption index before transfusion (p < .001). The individual increase in oxygen consumption index was inversely related to oxygen consumption index before transfusion (p < .001). Individual changes in cardiac index, oxygen delivery index, and oxygen consumption index were not significantly related to preoperative ejection fraction (25%-87%), age (32-81 yrs), and pretransfusion hemoglobin concentration (5.0-11.8 g/dL).

CONCLUSION

In adult patients after cardiovascular surgery, oxygen delivery- and oxygen consumption-related variables predict the individual response to blood transfusions better than do patient characteristics such as preoperative ejection fraction, age, and pretransfusion hemoglobin concentration. Including oxygen delivery and oxygen consumption, variables into the transfusion decision, thus, may enable a more individual use of allogeneic blood in specific situations.

Storage of whole blood before separation: the effect of temperature on red cell 2,3 DPG and the accumulation of lactate

BACKGROUND

Although whole blood intended for component preparation is commonly left to cool at ambient temperature, knowledge is insufficient as to the effects this may have on red cell quality, in particular after a prolonged hold.

STUDY DESIGN AND METHODS

Whole blood collected in ACD-A (7% wt/wt) and CPD (12% wt/wt) was incubated at 4, 10, 15, 20, 25, and 30 degrees C for 24 hours. Blood gases, pH, bicarbonate, glucose, lactate, and red cell 2,3 DPG were investigated.

RESULTS

When the blood was stored at 30 degrees C, the 2,3 DPG concentration decreased within 4 hours from 858 +/- 106 to 316 +/- 172 mmol per mol of hemoglobin (a 63% decrease); 99 percent was lost within 18 hours. At 25 degrees C, 46 percent was lost within 4 hours and 94 percent within 18 hours; at 20 degrees C, the decrease at 18 hours was 62 percent and that at 15 degrees C was 24 percent. No loss of 2,3 DPG was observed at 4 degrees C and 10 degrees C storage. No difference was attributable to the anticoagulant used. After 24 hours, the lactate concentration at 15 degrees C was 2.9 times the original, that at 20 degrees C was 3.8 times the original, that at 25 degrees C was 7.0 times, and that at 30 degrees C was 9.2 times.

CONCLUSIONS

With current anticoagulants, storage of whole blood at temperatures of 25 to 30 degrees C before separation causes a great and rapid loss of 2,3 DPG and an accumulation of acid metabolites. In a hold of blood for >4 hours, rapid cooling is desirable to avoid initial loss of 2,3 DPG.